Parse JSON data in Android

This tutorial describes how to parse JSON data in Android. JSON stands for (Java Script Object Notation). It is a simple and light-weight data interchange format that can be easily read by humans and machines. JSON is a text format that is language independent. It represents data in a text format so that can be easily parsed.
JSON is widely used nowadays and it is important to know how to use it and extract information. Almost all remote services use JSON to exchange data with a client. This tutorial explores how to parse JSON data in Android so that an Android app can call almost all remote services.

Getting started with JSON

The first structure can be used to model object because an object is a collection of attributes that hold some values. An Array can be used to model list, array of objects and so on. So using these two structures we can transfer data between two machines in a simple and efficient way. Lately, JSON is having a great success and most of the API available support JSON format. Let’s see how we can represent data in JSON.
An object in JSON is modeled using {..}, while its attributes can be modeled using name : value pair.Value can be, in turn, an object, an array or a “simple” value, like a primitive value (int, String, boolean and so on).
So if we have for example a java class like:

An array is represented in JSON using [..]. An array element can be an object, an array and so on.
Now we know a bit better JSON format, we can start using JSON with Android.

Using JSON in Android

In Android, and in general in all environments, there are two type of operation:

Convert java class to JSON data(Serialization)

Parse JSON data and create java classes (Deserialization)

Let’s suppose we have to send data to a remote server using HTTP connection and the data is represented in a java class. We have, as first step, convert java class to JSON data. As example, let’s suppose we have a class Person like this:

Let’s analyze the code. At line 6, we create a new JSON Object, it acts a container of our data. Next we put some name/value pair (line 7-8). As you can see they match the attribute of Person class. Looking at line 10 of Person class, we note we have an inner class, so we need another JSON object to reperesent it (line 10-13). When we have built our JSON object we put it in the main object line 16. At line 17, there is a phone List in our Person class. In this case we need an JSONArray to model the java List and for each item in the list we need JSON Object to map it. Running the source code available at the end of this post, we will have:

This is our JSON representation of our Person object. I used a nice web site that helps to test JSON data (http://www.jsontest.com/). As you can see from the result our JSON data is valid:

Parse JSON Data in Android: Deserialization

Another interesting aspect is parsing JSON data in Android and create Java classes. Even if there are automatic tools that create POJO classes from JSON data, it is important to know what’s behind. When you have a JSON data the first step is instantiating a parser that helps to get the values inside JSON.

JSONObject jObj = new JSONObject(data);

where data holds the JSON string. Now looking at JSON data file, we can start extracting data. For example, if we suppose that we get a JSON data like the one shown above (see JSON Person data), and we want to get the surname:

Using these pieces of code we can parse JSON data in Android. If you are interested about more complex JSON example give a look at Android weather app: JSON, HTTP and Openweathermap. Here it is explained how to create a full app that gets the current weather conditions.

About The Author

I'm an electronic engineer with over 15 years of
experience in computer programming. I'm the author of the book "Android things projects". I'm a MVB at DZone and DZone Guide Author. I have contributed to the IoT guide. I'm the technical reviewer of the book Internet of Things with Arduino Blueprints(published by PacktPub). I love creating IoT projects using Arduino, Raspberry Pi,
Android, and other platforms. I am interested in the convergence
between IoT and the mobile applications. I'm SCEA, SCWCD, and SCJP
certified.
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Simon MacDonald

It's a good tutorial to give people an idea of how to serialize/deserialize JSON but you may want to use the GSON library to reduce the amount of code you need to write.

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